Waste materials from electronic devices such as electronic substrates, flexible substrates, IC chips, mobile phones, or PCs, electrical appliances such as refrigerators, and automobiles contain combustible resin materials, iron (Fe), aluminum (Al), and other valuable metals such as copper (Cu), gold (Au), silver (Ag), platinum (Pt), and palladium (Pd). Therefore, techniques to reuse such waste materials as recyclable raw materials have been proposed.
Specifically, for example, the above-described waste materials are burned/melted (“burn/melt” in this specification refers to “burn and/or melt”) in a rotary kiln furnace to obtain a slag, and the slag discharged from the rotary kiln furnace is granulated to obtain a granulated lump. In the subsequent processes, this granulated lump is charged into a copper smelting furnace or the like and is smelted to recover the above-described valuable metals.
In the related art, techniques disclosed in PTLs 1 to 3 below are known as methods of treating recyclable raw materials in which raw materials containing valuable metals are charged into a rotary kiln furnace to be burned/melted.
In PTL 1, a basicity (weight ratio CaO/SiO2) of a slag (molten material) melted in a rotary kiln furnace is adjusted (the viscosity of the slag is decreased) by addition of a slag-melting agent containing CaO to increase the fluidity of the slag. As a result, due to a difference in specific gravity, molten metals are separated and discharged from the slag. In addition, considering corrosion resistance to the slag having such a high basicity, a brick (refractory product) which is composed of a basic magnesia-based refractory material containing MgO as a major component is used for an inner wall of a rotary kiln furnace.
In PTL 2, a water-containing sludge is added to waste materials (recyclable raw materials) containing metals charged into a rotary kiln furnace. As a result, the waste materials are gradually burned in the furnace to expand a burning zone in the furnace and to suppress a local temperature increase such that deterioration of a refractory product layer is prevented.
In PTL 3, an internal temperature of a rotary kiln furnace, which should be typically about 1400° C., is held at a low temperature of 600° C. to 700° C. to prevent the durability of the rotary kiln furnace from deteriorating due to overheating. Further, a stoker furnace is continuously provided on a downstream side of the rotary kiln furnace such that combustible materials are burned in two stages.
In addition, as disclosed in PTLs 1 to 3, typically, a burner for burning/melting recyclable raw materials and the like is provided inside a rotary kiln furnace.